In 1940 in a little Sicilian town on the day 12-year-old Renato experiences three major events: Italy enters World War II; he gets a new bike; and he first sees the beautiful and sensual young woman known as Malèna, who is the most desired of the town. Her husband is in the forces in Africa, fighting the British, and she lives alone. Because of her looks and her solitary state, she is an object of lust for all the town’s men and of hatred for its women. She keeps an eye on her infirm old father who lives alone, until he gets an anonymous note slandering her, upon which he rejects her.
Renato becomes obsessed with Malèna, spying on her in her house and stalking her when she leaves it. To fuel his erotic fantasies, he steals some of her underwear from her clothes line. When his parents find it in his bedroom, they go wild and try to break his fixation.
Malèna gets the news that her husband is killed, adding grief to her isolation. Rumours grow around her, which she unwisely helps by allowing an unmarried air force officer to visit her after dark. When she is denounced and put on trial, the officer sends testimony that he was nothing more than an occasional friend. The betrayal hurts, but Malèna says nothing to condemn him. After her acquittal, her advocate calls round and rapes her.
Renato decides to be Malèna’s protector, asking God and his saints to watch over her and performing little acts of vengeance against her detractors. He does not realise that his views of her are little better than those of the townspeople, and has no idea how Malèna herself feels.
Meanwhile, the war reaches Sicily and the town is bombed by the Allies, killing her father. Now penniless and universally scorned, with nobody willing to give her work, she sinks into prostitution. The townsfolk are happy to see her as a whore rather than a dangerous widow. When Nazi forces occupy the town and Renato encounters his idol with two German soldiers, he faints. His mother decides it is demonic possession, taking him to a priest for exorcism, but his more practical father takes the lad to the town brothel. There he fantasises that the prostitute initiating him is Malèna.
The Germans leave, and to ecstatic cheers American troops enter the town. The women storm the hotel and drag out Malèna, ripping off her clothes, beating her and cutting off her hair. To escape further persecution, she leaves the hostile town. A few days later, her husband Nino, who has survived as a prisoner of war but lost an arm, comes back looking for her. His house has been taken over by displaced people and nobody wants to tell him how to find his wife. Renato leaves him an anonymous note saying that she still loves him but has suffered misfortunes and gone to the city of Messina.
A year later, Nino and Malèna are strolling through the town. Women notice she now looks more matronly and plain. Even if she’s still beautiful, they realize that she is no longer a threat. So people begin speaking of her with more respect: when she goes to the market, the women who beat her say good morning and call her madam. Walking home, some fruit falls from her bag and Renato rushes to pick it up. He wishes her good luck and she gives him an enigmatic half-smile, the only time either has ever spoken to or looked openly at the other.
The aged Renato reflects that he has known and loved many women and has forgotten all of them. The only one he can never forget is Malèna.